Idiopathic thrombocytopenic purpura (ITP) is an acquired autoimmune disease with many immune dysfunctions. Cytotoxic T lymphocyte antigen 4 (CTLA-4) is a T-lymphocyte surface molecule that can down modulate and terminate immune responses. Recently, several studies have confirmed that some polymorphisms of this gene can influence its expression level, therefore speculating that they might be associated with autoimmune diseases. In order to investigate the role of the CTLA-4 gene in ITP, we investigated A49G polymorphism of the CTLA-4 gene in 30 ITP patients and 20 healthy controls through polymerase chain reaction (PCR)-restriction fragment length polymorphism. No significant differences were revealed in genotypes and allele distributions between the patients with ITP and the controls.